Synchronizing system for plural propellers with pitch and fuel control



June 4, 1957 T. A. BANNING, 1R 2,794,507

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SYNCHRONIZING SYSTEM FOR PLURAL. PROPELLERS WITH FITCH AND FUEL CONTROL Original Filed Jan. 18, 1945 14 Sheets-Sheet 12 FIG. 23

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United States Patent O SYNCHRONIZING SYSTEM FOR PLURAL PRO- PELLERS WITH PITCH AND FUEL CONTROL Thomas A. Banning, Jr., Chicago, lll.

Original application January 18, 1945, Serial No. 573,382.

Divided and this application September 26, 1951, Serial No. 248,340

36 Claims. (Cl. 170135.29)

This invention relates to improvements in controls for airplanes, and the like. The controls hereinafter disclosed relate to controls of power motor speed, blade pitch, throttle setting, and other functions of the power drive mechanism. These controls are for various purposes, including simplication of the pilots duties, and improvement generally in the power generation and delivery functions. feature and object of the invention relates to the provision of means to automa-tically cause the pitch and/or rotative sped of the propeller-motor units to automatically be adjusted continuously or from time to time to the pitch and rotative speed values which will maintain the speed of the ship at a predetermined value and under the conditions of maximum or optimum economy of ship movement. That is, the rotative speed and blade pitches are automatically adjusted continuously or from time to time to those values which will produce the maximum miles per gallon (or minimum gallons per mile) of ship ight at any pre-selected ship speed. This application is a division of my co-pending application for patent on lmprovements in Controlling the Pitch of Blades and Other Functions of Propellers of Multi-Motored Airplanes, and the Like, Serial No. 573,382, tiled January 18, 1945 now Patent No. 2,569,444, issued October 2, 1951. That application also makes reference to my co-pending application for patent on Improvements in synchronizing and Controlling Speed, Power, and other Functions of Multi- Motored Airplanes, and the Like, Serial No. 459,336, led September 22, 1942 now Patent No. 2,612,956, issued October 7, 1952. The present application, which is a division of Serial No. 573,3 82, will also make reference to Serial No. 459,336, especially as concerns certain disclosures of Serial No. 459,336 which are referred to in Serial No. 573,382, and as respects certain features of synchronization of speeds and powers.

The traction or driving force which will be exerted by a given propeller depends on various functions, including the rotative speed of such propeller, the bite or pitch which the blades occupy with respect to the fluid medium through which such propeller is travelling and against which such blades must exert their reaction, the density of the medium, air in the case of an airplane; and this density in turn depends principally on the elevation at which the plane is travelling above sea-level, and other factors. The power being transformed by the propeller into the useful work of driving the ship through the medium depends on the traction required for such drive (at the speed and under the various conditions then subsisting), multiplied by such speed, and the power developed by the power motors is of course a function of this useful power, that is, it is the useful power divided by the eiciency of transformation between the power motor (or motors) and the medium through which the ship is travelling.

It is well known that the transformation efliciency of a propeller is a direct function of the pitch at which such propellers blades are set (taking account of the free As will appear hereinafter, a very importantice flight velocity of the ship in the air), and is also a function of the rotational velocity of such propeller, for given conditions of the medium, such as density, contained moisture, etc. The characteristic curve of etlciency of such a propeller, for a given set of conditions of ,rotational speed, density of the medium, etc., rises as pitch is in-v creased, to a relatively at top portion of the curve, and thereafter descends to zero when the pitch has been raised to a characteristic maximum. The free flight velocity of the ship through such medium also affects the form of this curve. For each set of specified conditions of operation (rotational speed, density of medium, etc.) there is a characteristic curve, and a family of these curves can be plotted for such specified set of conditions.

It is also well know that the characteristic curve of traction vs. pitch for such propeller, under a given set of conditions of rotational speed, density of medium, etc., rises from zero for a certain pitch setting of the blades (taking account of the free flight velocity through the medium), to a maximum, which is rather sharply defined in the cases of most propellers of conventional design, and thereafter descends, generally on aV curve which is concave upwards, to zero again for a characteristic high pitch angle. Therefore for such specified set of operatingA conditions and other conditions affecting the ight o'f the body through the medium the maximum traction Vor driving force is developed at a specified pitch angle of the propellers blades, and relatively small departures from such pitch angle setting will result in very substantial reductions of traction and changes of overall eiiiciency. It is therefore much to be desired that the operations be performed as near this optimum condition of pitch angle as possible in order to secure from the equipment a maximum of effective power transformation, and therefore a maximum of work economy. It must be here observed also that changes of rotational speed will affect the form of the characteristic curve, the pitch at which maximum traction is developed, and the maximum overall efficiency and economy which may be attained for any pre-selected ship speed. Accordingly, both blade pitch and rotational speed must be considered in determining those operational conditions which will result in moving the ship through, the medium at the pre-selected speed and with least rate of fuel consumption and corresponding least fuel consumption per mile traversed. Y

Change of the specified operating conditions, includingy rotational speed, density of medium, etc., results in change,

of the characteristic curve of traction vs. pitch, and produces change in maximum traction which will be developed, as well as change in the angle at which suchlt is thus possible to plot a farnily` maximum will occur. of such characteristic curves of traction vs. pitch, such family being for changes of rotational speed, and otherk families of like nature may be plotted for other changes of specified conditions, such as density of the supporting medium, etc.

In the case of a multi-motored ship (airplane,'for ex' ample) the various power units should be synchronized so that they will all operate under the same specified conditions of operation. These operating conditions include rotational speed, developed power, pitch angles,

traction developed, and other functions.' The prior artY q t D chronizations are also disclosed in said cri-pending application, Serial No. 459,336, Patent No. 2,612,956.

It is evident that various groupings of controls may be eifected. Thus, control of rotational speed vs. tractive effort or driving force may be secured; or control of rotational speed vs. blade pitch may be secured; or control of rotational speed vs. free flight velocity may be secured; or various other combinations of controls may be secured according to the desired vultimate or end control which is sought. In each of these combinations of controls, or in all of them, it may also be desired to malte provision for securing a specified end result, in this, that a specified developed (or transformed) power may be desired, or a specified traction or driving force may be desired; and since production of either such specified power or traction entails controls of two or more functions it is evident that joint controls of such several factors must be made in proper relationship, that is, as one factor is changed, the other factor or factors must be simultaneously changed, and such simultaneous changes must be of proper amounts and in proper directions to still produce the desired end result. The production of such multiple changes may be effected manually, either by individual controls for the several power'units, or in gang; but such manual controls become more and more complex and diicult to interrelate, with increasing complexity due to increasing numbers of propellers and power units for larger and larger ships.

It is an object of the present invention to make pro vision for joint controls of two or more of the essential functions ofthe power units, such as joint control of rotational speed vs. traction or driving force, for specified power developed, or joint control of rotational speed vs. blade pitch of the propellers, for specified traction or driving force developed, or other forms of joint controls. It is a further object of the invention to elfect such several joint controls with simultaneous synchronization of the proper functions of the several power units to ensure properly synchronized operations, and under the joint controls selected. Y

More specifically, and as an important feature of the present invention, it is an object to secure joint controls of the selected functions for specified or adjusted condi- 'tions' of rotational speed vs 'free flight velocity of the ship within the supporting medium. While maintaining specified rotationalr speed of the propeller or propellers, maintainance of specified free iiight velocity requires adjustment'of blade pitch from time to time to maintain the traction requisite for such free ight velocity, and it is an object of the invention to make provision for securing such result. In case of change of various ight conditions the attainment of the optimum condition of least fuel consumptionY per mile traversed may and probably will require change of rotational speed as Well as pitch. The following disclosures include thev means to effect such changes automatically. In case of change of the specified free ight velocity by a control unit which determines such free iight velocity the rotational speed or the blade pitch or both, may and probably will require change in order to maintain the, ship at such changed free iiight velocity under the optimum condition of at least fuel consumption per mile traversed. The disclosures herein contained embody the means to attain those results. lt is a further object in this vconnection to secure the foregoing results while at the same time ensuring synchronization of propeller rotational speeds; and a further object in this connection is to secure this result While maintaining synchronization of powers developed by the several powermotors. In this case the driving force exerted on the ship as a whole is always the summation of the driving forces exerted by all the power motor units in service, and that total driving force is to be maintained at value correct to maintain the .desired and pre-selected free tiight velocity of the ship.

It is a further object to producev the results just above enumerated with synchronization of powers of the several power units, such power synchronization of powers being produced either by throttle controls or by blade pitch controls of the several power units.

A further and important feature of the present invention relates to the provision o f a joint control arrangement such that the free ight velocity of the ship may be maintained automatically at a specified or pre-selected value, with a minimumy consumption of fuel by the power motors. For example, if it be desired to maintain a free iliglit velocity of selected value, such as 400 miles per hour, it is an object of the invention to provide means whereby such pre-selected and pre-set velocity of the ship will be maintained with the power motors and propellers operating under those conditions which will require a minimum consumption of fuel at all times, thereby making it possible to drive the ship between selected terminals with a minimum consumption of fuel, while maintaining such pre-selectedtfree flight velocity, to thus ensure maintainence of a selected schedule. c

In connection with the foregoing it will be recalled that pitch variation results in change of etiiciency of the motor-propeller unit considered as a power converting unit, and therefore change of pitchfunder specified operating conditions results in change'of such conversionV efhciency; or, viewing the matter from another angle, in order to maintain maximum conversion efficiency it is desirable to be able to operate the propellers at all times under such conditions as to voperate at the peak of the elicieucy characteristic curve of the motor-propeller units. Since for any given motor propeller unit there exists a family of such characteristic curves of efficiency vs. pitch angle, it follows that whenever the several operating conditions, such as rotational speed, density of medium, etc. change it becomes necessary to change the propeller pitch and for rotational speed in order to maintain the maximum or optimum eciency condtion of power conversion, while still maintaining the pre-selected free flight Velocity of the ship. It is an object of the present invention to make provision for securing this result at all times, fully automatically, after the pilot has brought his ship into free flight condition, and with the sole requirement that the pilot pre-set the ship speed control to the Y desired free iiight velocity. Thereby it will be possible to drive the ship between two selected terminii at a preselected average speed, and with a minimum of fuel conconsumption. It is a further object in this connection to provide means whereby this result may be secured while maintaining synchronism of the several power units for rotational speed, developed powers, and blade pitches of their respective elements.

It is a further object in connection with the foregoing feature to make provision for such synchronization by use of previously devised and well known forms of synchronizing means, thus adapting the features of the present invention to previously known and used forms of such synchronizing elements, while still securing the desired objects of the present invention.

It is a further object in connection with the foregoing object `of providing means to secure free iiight Velocity at optimum economy conditions, to make provision for synchronizing the several propellers for blade pitch, that is, to secure said result with further provision-for ensuring that the pitches of the blades of the several propellers are synchronized atV all times, so that they are all operating under the same conditions of pitch adjustment.

A further feature of the present ,invention is to provide a special unit which is capable of detecting'departure of the operatingtconditions ofthe power units from those conditions which give optimum economy of operation,

and which unit is provided with means to make such cor-V rections as are needed to restore the operating conditions of the power units to the maximum or optimum economy conditions, namely, those conditions under which the.,

minimum fuel consumption is demanded consistent Y,with

maintainence of the pre-selected free ight velocity condition,

Specifically this economy detection unit is so arranged as to continuously determine the ratio of free ght velocity to fuel consumption, and to continuously set its movable control to a position or changing position corresponding to such changing ratio, and is further provided with means to then effect the required corrections of operating conditions to restore the ratio so determined to the maximum or optimum condition attainable for the selected and pre-set free flight velocity, and taking into account the fact that the characteristic curve of economy vs. pitch angle depends on the factors of free flight velocity selected, density of medium, and other factors, and also taking into account the fact that each such curve of a family of such curves carries its own peak value and pitch position. This means also takes account of the fact that characteristic curves of economy vs. propeller rotational speeds carry peaks, and that there is a family of such curves for each selected set of operating conditions, and said means makes provision for continuously selecting the values of the variables (propeller rotational speed and propeller pitch) which will ensure maximum economy of operation for the then existing operating conditions of the propeller or propellers.

Other objects and uses of the invention will appear from a detailed description of the same, which consists in the features of construction and combinations of parts hereinafter described and claimed.

In the drawings:

Figure 1 shows a typical characteristic curve of traction vs. blade pitch, showing how the traction rises with increase of pitch up to a peak value and then descends as the pitch is increased further;

Figure 2 shows a typical characteristic curve of traction vs. blade pitch, showing a modified curve which is typical of a form of blade pitch control device in which there is provided a spring element working on the blade stub carrier in the direction of traction produced by the ro-l tation of the propeller itself as shown for example in my cci-pending application Serial No. 573,382, now Patent No. 2,569,444, of which case the present application is a division;

Figure 3 shows a fragmentary longitudinal section through a blade pitch control device in which the blade stubs are carried by an element which may be shifted back and forth on the propeller shaft, against or with the direction of traction produced by the propeller, and in which such movements serve to vary the blade pitch with reduction of pitch with movement in the direction of traction, and in which device the traction produced by the rotation of the propeller is balanced by a controllable but uniform resistance in the form of a movable abutment the value of whose resistance to movement is controllable, and remains constant as said abutment moves back and forth at such adjusted value or amount;

Figure 4 shows a cross-section taken on the line 4-4 of Figure 3, looking in the direction of the arrows, the blade stub carrier being in its rearmost position, and with the blade pitch at maximum value;

Figure 5 shows a cross-section similar to that of Figure 4, and also taken on the line 5-5 of Figure 4 looking in the direction of the arrows, but with the blade stub carrier shifted forwardly to its full forward position and with the blade pitch correspondingly reduced to a low or zero value;

Figure 6 shows a longitudinal section through a form of pressure reducing valve which is capable of maintaining the fluid pressure on the delivery end of such valve at a constant but adjustable value, even for flows of fluid away from or back to such valve from a receiving element or device ,and when there is connected to said valve a source of fluid pressure at least as great as the desired delivery pressure;

Figure 7 shows a cross-section taken on the line 7-'7 of Figure 6, looking in the direction of the arrows;

Figure 8 shows schematically one set of oil or uid connections for control of the blades of a set of propellers having variable pitch blades, which blades are shiftable in direction parallel to the direction of traction produced by such propeller, and which propellers are provided with movable abutments which establish constant but controllable resistances to movement under such traction force, which resistances may be controlled or re-set in value from time to time; and this igure shows a gang control arrangement such that the tractions of all the propellers of such gang may be simultaneously controlled for a selected traction value by use of a single valve;

Figure 9 shows another schematic arrangement, wherein each of the propellers may be individually controlled from its individual control valve;

Figure 10 shows still another schematic arrangement, wherein both pusher and puller propellers are provided in two gangs, each gaing being individually controlled by its own control valve;

Figure ll shows still another schematic arrangement, wherein the propellers embodying features of the present disclosures may be used in connection with a form of servo-motor device which is capable of ensuring true synchronism of pitch of the blades of a number of variable pitch blade propellers;

Figure 12 shows more or less schematically a joint control for two of the functions, namely speed and traction or driving force enabling control and synchronization of these two functions by use of a single control handle or button convenient to the pilot or operator; said joint control being suitably marked to show these functions, and also being provided with supplemental markings or iso-lines to indicate lines of equal power developed by the power-motor-propelled ship;

Figure 13 shows more or less schematically another joint control similar to that of Figure 12, but for controlling and synchronizing speed and pitch of propeller blades by use of a single control handle or button; and being suitably marked corresponding to these functions, and also being provided with lines or iso-lines to indicate lines of equal traction or driving force;

Figure 14 shows another schematic arrangment as a modification of that of Figure 13, and for controlling speed and pitch by another form of pitch control and synchronizing than that of Figure 13;

Figure 15 shows schematically a control arrangement whereby by use of a single control handle the rotative speed of the power-motor-propeller units during takeoff may be preset, and whereby the air speed of free-flight may also be preset, the arrangement being such that synchronism of all the units will be automatically maintained, and whereby the pitches of the propeller blades will at all times be automatically maintained and controlled at those values proper for the pre-set conditions of operation, and the arrangement also making provision for certain other desirable results and features of operation; and this figure also indicates the connections from the units shown in this gure to the meters which meter the rate of fuel supply to the several power motors and comprise a portion of the synchronizing and controlling means, said meters and associated elements being fully illustrated and disclosed in the aforesaid application Serial No. 459,336, now Patent No. 2,612,956.

Figure 16 shows schematically a simple form of airspeed pitch control unit for use in connection with the scheme of Figure 15 Figure 17 shows in simple form a oW-shee or diagram illustrating the sequences of transfers of elects from various units of the arrangement of ligure 15 to other units of that scheme;

Figure 18 shows schematically another control arrangement incorporating certain of the features of the scheme of Figures 15, 16 and 17, but making use of elec- Varcanos' trical units for 4eflectingthe actual blade pitch changes, said units being of well known type, and being combined with other elements and units of the present invention in a novel manner to produce new and unexpected results; andrthis ligure also indicates the connections from the units shown in this figure to the meters which meter the ratel of fuel lsupply to the several power motors and comprise a portion of the synchronizing and controlling means, said meters and associated elements being fully illustrated and disclosed in the aforesaid application Serial No. 459,336, now Patent No. 2,612,956.

Figure 19 shows schematically another control scheme in which the setting of the free-flight velocity handle serves to ensure delivery at all times of that amount of power, within the power range of the several power motors, necessary to maintain such pre-determined freeflight velocity of the airplane, provision being made for synchronizinz the power-motor speeds, and also for spnchronizing the powers delivered by the several powermotors while maintaining such pre-determined free-night velocity this figure showing the connections from the units shown in this figure to the meters which meter the rate of fuel supply to the several power motors and comprise a portion of the synchronizing and controlling means, said meters and associated elements being fully illustrated andl disclosed in the aforesaid application Serial No. 459,336, now Patent No. 2,162,956;

Figure 20 shows several typical performance curves of an airplane equipped with propellers, and shows how the economy of operation, over-all, may vary under diierent operating conditions (such as variation of blade pitch, variation of height above set-level etc.), with variation of rotational speed of the propellers, these curves constituting a family of such performance or characteristic curves;

Figure 2l shows a schematic layout of what I here term an Econometer unit by which provision has been made for automatically comparing free-night velocity with rate of fuel consumption, to determine the economy of operation (as an example in gallons per mile or in miles per gallon or per hundred gallons), and for automatically readjusting the power-motor speeds or blade pitches from time to time to maintain these speeds or pitches at the values, which will give maximum economy of operation, s'o that the pre-selected velocity of free-flight may be maintained under the conditions of least fuel consumption consistent with the then existing operating conditions; the scheme of Figure 2l being usable in connection with that of Figure 1G, for example, as well as Figures 22, 23 and 24, to establish a complete layout for also automatically controlling and synchronizing propeller blade pitches, power-motor generated powers, and other functions of the problem;

Figure 22 shows schematically an arrangement wherein the setting of the control handle for free-flight velocity serves to effect control and synchronization of powermotor powers to maintain that desired free-Hight velocity, and wherein the rotative speeds of the several powermotors are controlled and also synchronized by the functioning of the econometerj such as that shown in Figure 2l, use being made of hydraulic blade-pitch controls incorporating relays such as the type shown in Letters Patent, No. 2,217,856, to Brady, by way of example only, the blade-pitches of the several propellers in Figure 22 being individually controlled; and this ligure also indicates the connections from the units shown in this figure to the meters which meter the rate of fuel supply to the several power motors and comprise a portion of the synchronizing and controlling means, said meters and associated elements being fully illustrated and disclosed in the aforesaid application Serial No. 459,336, now Patent No. 2,612,956;

Figure 23 shows schematically an arrangement wherein the setting of the control'handle for free-flight velocity serves to effect control and synchronization of the pitches of the blades or" the several propellers to maintain that desired free-flight velocity, and wherein the rotative speeds of the several power-motors are controlled and also synchronized by operation of the econometer, such as that shown in Figure 21, use being made of gang hydraulic blade-pitch control, for example, such as shown in Figures 3, 4 and 5 of this case; the blade-pitchesbeing automatically balanced against traction of driving force needed to maintain the desired free-flight velocity; and this figure also indicates the connections from the units shown in this figifzre the meters which meter the rate of fuel supply to the several power motors and comprise a portion of the synchronizing and controlling means, said meters and associated elements being fully illustrated and disclosed in the aforesaid application Serial No. 459,336, now Patent No. 2,612,956.

Figure 24 shows schematically an arrangement wherein the setting of the control handle for free-flight velocity serves to effect control and synchronization of powermotor speeds to maintain that free-flight velocity, and wherein the pitches of the blades of the several propellers are controlled by the econometer, such as that of Figure 21, use being made of blade-pitch synchronization such as that of Figure ll of the present case; and this ligure also indicates the connections from the units shown in this figure to the meters which meter the rate of fuel supply to the several power motors and comprise a portion of the synchronizing and controlling means, said meters and associated elements being fully illustrated and disclosed in the aforesaid application Serial No. 459,336, now Patent No. 2,612,956;

Figure 25 shows a modication or detail wherein there is provided a fuel meter in the main fuel supply line to determine rate of fuel consumption for operation of the econometer of Figure 2l;

` Figure 26 shows a modification of Figure 22 wherein use is made of synchronizing control units of the type shown in my co-pending application, Serial No. 459,336, now Patent No. 2,612,956; and

Figure 27 shows a set of typical characteristic curves of relation of propeller eiciency to blade-pitch thereof, being a family of such curves.

In a convention application of the features of the present invention which are concerned with the provision of automatic controls to produce the maximum economy in miles per gallon or minimum gallons per mile, when the propulsion means includes variable pitch propellers, I contemplate the application of said features of invention to such variable pitch drives without limitation to any specic arrangement of pitch control, per se, except as I may limit myself in the claims to follow. I have, however, in the present application, by way of example of one form of variable pitch arrangement, shown a variable pitch propeller of the general type also shown in said application Serial No. 573,382, now Patent No. 2,569,444. For convenience I shall iirst describe such variable pitch construction as follows:

The blade pitch control device shown in Figures 3, 4 and 5 hereof, by way of illustration, only, is of such construction that the traction or driving force developed by the propeller rotation tends to shift the blade stub carrier in the direction of such traction with a force proportionate to such traction, and this control device is also provided with means to resist such movement of the blade stub carrier by imposition of a controlled amount of force to resist such movement. Such controlled force is so exerted that the blade stub carrier is nevertheless able to actually effect such movement in the direction of the developed traction, but the arrangement is such that said controlled resisting force is maintained constant during such movement. The movement of the blade stub carrier also serves to change pitch angle, such change being a reduction of pitch angle when the movement is in the direction of the tractive force, and being an increase of pitch angle when the movement is against the direction of the tractive force. All such effective movements are produced only within that range of pitch angles of the characteristic curve in which increase of pitch angle causes increase of tractive force, that is, on the rising portion of the characteristic curve. This control device of Figures 3, 4 and 5 is also provided with means to take care of blade stub carrier movements beyond such rising portion of the characteristic curve, so that the device can never move to a position where control is lost. The device shown in Figures 3, 4 and 5 is also shown in my co-pending application, Serial No. 573,382, now Patent No. 2,569,444, of which the present case is a division.

Reference may now be had to Figure 1 which is a typical characteristic curve of variation of traction or driving force developed by a given propeller, with change of pitch angle of its blades. Since the blade form is generally one of varying pitch measured from hub to tip, such curve is conventionally plotted to show the Variation of the basis of pitch at .75 radius; and the curve 231 of Figure l is a typical curve plotted on that premise. Furthermore, the traction or pull developed by a given propeller will of course depend on the rate of rotation thereof, and the curve of Figure 1 is based on the normal operating speed of the propeller in question.

It will be noted that the traction or pull rises with increase of pitch up to a maximum amount at 12 to 15 degrees, and then falls to zero at substantially 90 degrees pitch. We may assume then that the full feathering position is at 90 degrees, and the drifting position is likewise at that angle. It is also noted that traction rapidly rises from zero degrees to about 12 to 15 degrees, and then falls rapidly for about 15 degrees with a reducing rate of such fall. Reference may now be had to Figures 3, 4 and 5.

In these figures the end portion of the engine shaft is shown at 232. This may be either the engine shaft proper or may be gear driven from the engine shaft as desired. Secured to this shaft end is the hub member 233, for which purpose the adjoining ends are anged as shown at 234 and 235 so that they may be secured together in suitable manner. The hub member 233 is hollow to its closed outer end 236; and a collar 237 is slidably mounted on such hollow hub. This collar carries the radially extending blade stub receivers 238, 239 and 240 (239 and 240 not appearing in Figures 3, 4 and 5), three such blade stub receivers being mentioned by way of illustration, only. The blade stubs are received in these receivers, and blade stub 241, only, is shown.v This blade stub is provided with the annularly outwardly facing shoulders 244 which engage with corresponding reversely facing shoulders of the blade stub receiver to prevent possible out-throw of the blade during running. In the porm shown I also provide a ball bearing 245 (not shown in the figures) around the stub adjacent to the outer end of each retainer; and a thrust roller bearing 246 is placed around the inner end of each stubto normally take the centrifugal force created by the rapid rotation of the propeller. In case of emergency the shoulders 244 will prevent outthrow of the blades, but normally the roller bearing takes the force of the centrifugal operation, and the ball bearing retains the blade stub in alignment. Thus the blade stub may be easily rotated for pitch control.

The inner end of each blade stub is squared as shown at 247, and a circular plate 248 is pinned thereon by an ample cross-section pin 249, so that during running this circular plate bears against the inner race-way of the roller bearing to transmit thrust thereto. This circular plate has at one side an extension 250 which constitutes a crank arm, as will presently appear. A link 251 has its inner end pinned to such crank arm by the pin 252, and said link extends out from the stub retainer to a position adjacent to the end of the hub member 233 where said link is pivoted as shown at 253. It will now be seen that since the collar 237 is slidingly mounted on the hub member 233 so that it can shift back and forth,

10 such shiftings will cause the blade stub to rock with a movement dependent on the extent of sliding movement, the proportions of the crank arm and link lengths and other factors as will be readily apparent.

Within the hollow hub there is slidingly mounted the plunger 254 having the rod 255 which reaches back towards the engine, and said rod 255 is hollow so that oil or other fluid may be placed under pressure against the outer face of the plunger by communication through said hollow rod 255. Said rod 255 works into the passage 256 of the engine shaft 232 with an oil tight fit, preferably sealed by the gland 257 and communication is established between the passage 256 and the outside of the engine shaft by means of the stationary collar 253 having the internal groove 259 communicating with the outwardly extending opening 260 from the passage 256. Thus pressure exerted against the front face of the plunger 254 is controlled from outside the structure and by connection to the collar 258. Such connection is established by the nipple 261.

Now it will be seen that during normal running of the propeller the traction or pull thereof is towards the right in Figure 3 so that oil pressure built up against the front face of the plunger resists such traction, and by setting the oil pressure at a given or predetermined amount the traction which must be generated by the running of the propeller to cause shift towards the right in Figure 3 may be controlled to a desired value. It will also be seen that back and forth movements of the propeller hub and blade stubs are necessarily accompanied by shifts of blade angle or pitch of the blades, due to the link connections already explained.

It is intended that the parts shall be so proportioned that normal tractions exerted by the propeller may be resisted by the oil or fluid pressure with reasonable pressures such as tiftyto one hundred pounds per square inch, but the exact proportions will be a matter of individual design. It is furthermore noted that the amount of shift of the hub member 233 provided is sufficient to permit full throw of the blades from Full feathering to Zero pitch angle, being a throw of substantially ninety degrees. It is also noted that the parts should generally be so arranged that when the hub member 233 is in its full forward position the blades are in the zero pitch angle position, and that when the hub member is shifted full backwards the blades are in their full feathering position, a rock of substantially ninety degrees. In Figure 5 the parts are shown in full feathering position, as shown by the arrow 254, and the crank 250 lies somewhat forward of the radial line; in Figure 4 the parts are shown in the full traction angle position, the arrow 263 showing a tilt of substantially fifteen degrees or slightly more (rotation being clockwise when viewed from in front of the propeller), and the crank arm 250 is at substantially right angles (somewhat less) to its position in Figure 5. It will also be seen that in changing from the position of Figure 5 to that of Figure 4 the blade has suffered a pitch angle change of somewhat less than ninety degrees. Another movement counterclockwise (when viewed as in Figures 5 and 4) is provided for, so that the crank arm 250 would move still further over (counterclockwise) than the position shown in Figure 5, and into a reversing pitch angle position. During the full rocking movement the crank arm has suffered a rock of ninety degrees, but at no time has such crank arm been in a dead-center position with respect to the link 251 and pivot pin 253, so that shifts are at all times readily eected. It will also be seen that such shifts of blade pitch have been effected merely by back and forth sliding of the sleeve 237 on the hollow hub. It is furthermore noted that the arrangement is such that such shiftings are effected in such manner that the tendency of the traction or pull of the propeller itself is to cause a reduction of blade pitch, since forward movement of.

the sleeve 237 due to pull or traction of the propeller 11 tends to vrock the blades back towards the zero-pitch position, reducing pitch thereby. It is further seen that such reducing tendency is resisted by the oil pressure against the front face of the plunger 254.

From all the foregoing it is now evident that by setting the oil pressure against the front face of the plunger at a predetermined value by means of a device which will maintain such pressure value while at the same time allowing for oil movements due to back and forth shiftings of the plunger 255i, we shall be able to automatically maintain the propeller with a predetermined pull or traction, dependent on the established oil pressure, and any condition which tends to increase the pull or traction will automatically cause the propeller to shift to a position where that traction is again developed, or vice versa. It is, however, to be noted that in case it is desired to maintain the blade pitches at a given value irrespective of pull or traction being developed, this result may be secured by forcing oil into the cylindrical space before the plunger 254, and locking said oil therein, to thereby maintain the blades at the predetermined pitch and without allowing them to shift back. to a condition of lesser pitch.

It is also noted that this arrangement is such that the tendency of the pull or traction is always to reduce pitch, and that the total force which must be resisted by the pressure of the oil against the plunger face is equal to the total traction or pull being developed by the propeller. Also, that the traction or pull of the propeller is transmitted to the hub for transmission to the airplane, through the medium of the oil and plunger arrangement. This result is secured as follows:

The plunger rod 255 carries a collar 265 having the outwardly extending arms such as 267, which reach through the slots such as 279 of the hub member 233, and the outer ends of these arms are received in notches such as 273 of the collar 237. The ring 275 is threaded onto the end portion of said collar to retain said outer arm ends in place in such notches, and to lock the parts together. lt is here noted that for purposes of assembly the ring 275 is also provided with notches such as 276,

which will pass the outer ends of the arms during assembling of the parts; but said ring should then be brought to a final position of rotation such that the outer ends of the arms are locked in position as shown in Figure 3. It is thus seen that these arms perform two functions; they transmit forces of rotation from the hub member 233 to the blade stub receivers, and thus drive the'blades; and also they transmit pull or traction forces from the blades to the hub member, and thus secure the transmission of the traction or pull to the airplane; and all I prefer to split the blade stub receivers, one portion 279 of each of them comprising a portion of the collar 237; and the other portion 28d) of each of these blade stub receivers being secured in place by suitable means such as screws or the like. Preferably, also, such splitting is effected on a plane normal to the axis of rotation, as shown in the figures. Furthermore, a collar, not shown, may be threaded onto the outer ends of these split por# tions to further assist in holding them together.

In Figure 3, in particular, I have shown the Sylphon 282 placed within the cylindrical chamber `of the hub member 233 and in front of the plunger, and a tubular extension 283 of this Syiphon is carried through the hollow rod 255 to its rear end where it may be brazed or otherwise sealed thereto. Use of such Sylphon arrangement Will provide a perfectly oil tight construction, and one which can be readily assembled. In the absence of such Sylphon arrangement the plunger 254 may be provided with the piston ring 284 of suitable form for sealing against liquid leakage.

Now in the operation of this scheme it is intended that oil or other tiuid pressure should be exerted in the space in front of the plunger` of pressure depending upon the traction or pull which it is desired to exert by the propeller, so that upon bringing the propeller into operation it will commence generating traction, which will increase with speed or until the condition of balance is found. Or, the propeller may be iirst brought to speed without creation of such pressure against the front face of the plunger, so that the generation of a slight amount of traction or pull by the propeller rotation will set the same forward substantially to the zero-pitch angle position where substantially no traction Will be developed even at speed. Then, by building up the oil or other fluid pressure the propeller will be successively forced back to a condition of balance dependent on such pressure so established, or dependent on the position at which the propeller is locked.

Reference to the curve of Figure l shows that the maximum traction which will be developed (under selected conditions of speed) will be attained long before the position of degrees is reached; and in case of operation at or near the peak 285 of such curve it is evident that reduction of traction (or pressure) might be accomplished either by reduction or increase of pitch. Thus,.if we should be operating near such peak position, with the oil pressure suicient to maintain the pitch at the corresponding degree position, a reduction of such oil pressure might result in increase of pitch rather than decrease thereof, as desired. T o prevent such a condition, and for other reasons, I have provided behind the plunger 254, one or more springs whose accumulated strength is sufiicient, at the proper time, to ensure that the collar 237 and blade stub receivers, will always be returned to the lesser pitch condition upon reduction of oil pressure. These are the springs 286. They occupy positions between the back face of the plunger and the front end of the shaft section 232.

Now it will be seen that the force of these springs must be overcome in addition to that of traction or pull exerted by the propeller blades, in order to maintain the collar 233 at any given position, so if the effect `of these springs is exerted prior to the time the peak of the curve 237 is reached (Figure l) such force must be added to that of traction, in setting the bla-des to a given pitch position. But the effect of these springs is not generally required until at or near the peak condition. Therefore I prefer to so set these springs, and to use springs of such characteristics, that they will not come into operation until the plunger has moved back a distance suiiicient to cause the blades to assume la pitch value which is slightly less than the pitch for maximum traction, such maximum traction pitch being the pitch at the point 285 in Figure 1. This may be done, for example, by so forming these spr-ings that they are fully extended at or about the time the plunger stands at a position slightly prior to reaching the peak condition, yso that further movement to the left (Figure 3) will cause compression of the springs thus adding their effect to that of traction or pull of the blades. Furthermore, `from that time on it is noted that the effect of `such spring should be to require fa continuously increasing pressure from the plunger, so that the 'additive effect of springs and traction or pull `of the blades will 'always 'be to cause a rise of their additive curve. Thus, in Figure 2 I have repeated the curve 231; and I have valso shown by the curve 287 the effect of the spring or springs. Their cumulative effect is shown by the curve 288 which rises continuously from 'a position near the peak 285 to a still ever higher position, so that as the plunger continues to move to the left beyond the peak position the curve will continue to rise. By this means there is assurance that Whenever the plunger is forced beyond the peak position it will, when the oil pressure is again reduced, move back towards the lesser pitch condition, instead of continuing on over to the Full feathering or 99 degree 

